Which command will need to be added to External_A to ensure that it will take over if serial 0/0 on

Which command will need to be added to External_A to ensure that it will take over if serial 0/0 on External_B fails?

Select the best response.

A.
standby 1 preempt

B.
standby 1 track 10.10.10.1

C.
standby 1 priority 130

D.
standby 1 track fastethernet 0/0